This would be brittle. Take all my arguments against the ^this feature
discussed in an earlier thread and repeat them here. Labels work just fine (and
better than numbers would) for this purpose.
Dave
On Apr 9, 2011, at 7:32 AM, Bradley Meck wrote:
> I think since we can only break/continue to labels in a linear chain
> upwards, break could take a number for how many loops it should break.
> This could still be tested at compile time as well, but would lead to
> somewhat less readable code. It would however be incompatible with
> current label based breaks (easier to find an replace if a compiler
> warns you).
>
> while(true) {
> while(true) {
> break 2;
> }
> }
>
>
> Anywho, I don't personally like number based breaking, just throwing
> around ideas.
>
> Cheers,
> Bradley
>
> On Sat, Apr 9, 2011 at 4:10 AM, Claus Reinke <[email protected]> wrote:
>>> Can we remove labels from the next version of the spec?
>>
>> I'm not a fan of labels, at least not as a built-in language
>> construct - I'd much prefer if the language was expressive enough to emulate
>> such functionality when needed (that
>> includes useable syntax), not to mention reducing the
>> need for such features in the first place.
>> However, as long as Javascript has break and continue, ..
>>
>>> Am I missing anything? Or are there cases where labels allow you do
>>> something that's impossible without labels?
>>
>> It seems that language features like lambdas have been shot
>> down because of their interaction with break and continue.
>> In brief, people want to be able to abstract over syntax phrases
>> like the one marked with -| .. |- here, by wrapping it in some
>> form of immediately called function and still have it behave as before:
>>
>> while (..) { .. -| break; |- .. }
>>
>> [aside: as far as I understand Tennent, this has nothing to do
>> with his principles of correspondence or abstraction, which
>> are often misquoted and conjured with in the archives]
>>
>> Now, if we want to wrap that phrase into a function (not a
>> syntax macro), then that function cuts through the while/break
>> construct. Still, we can refactor the code a little to make that
>> wrapping possible:
>>
>> loop: while (..) { .. switch ( -| function() { return 'break'; } ()
>> |- ) {
>> case 'break' : break loop;
>> case 'continue' : continue loop;
>> }
>> .. }
>>
>> With this change, we are able to wrap code involving break
>> or continue into a function (and move that function definition
>> out of the loop body). Since the switch statement has its own
>> break-target, we need the loop label, even though the original
>> break did not have a label.
>>
>> There are other ways to handle this situation, but this seemed
>> to be the most direct way of expressing the intention, given that labels are
>> not first-class values in Javascript.
>>
>> Better alternatives welcome,
>> Claus
>>
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>>
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